I've heard all (except the supersprint), and my current favorite is the Eisenmann Race. It sounds bigger, badder and better than the others and its only an axle back setup! No performance gains though...so depends on what you're looking for.

I'm very curious about the Supersprint, but there is seemingly very little info about it anywhere.

IMO, you cant go wrong with any of the current offerings available. All of them are a bit different in what options they offer in terms of tip size, functionality, power, but a better sound is the end result of all of them and that improves the overall experience as the car is really screaming for an exhaust.